This invention is directed generally to the field of horizontally-fired industrial boilers which burn an ash-laden fuel in suspension, and more particularly to a novel means for permitting ash to be removed from such a boiler system without requiring the shutting down or even the reduction of the output of the boiler system.
In many applications, it has been found to be advantageous to prefabricate an industrial boiler system at a factory rather than building it at the site where it is to be used. The size of such systems, however, is generally limited by the capabilities of the method of transportation of the prefabricated boiler system to the site. Often such systems are limited to the maximum size that a conventional railroad freight car can carry within the clearance restrictions of the route.
It has also been found to be advantageous to use an ash-laden fuel such as pulverized coal, for example, because often it is substantially cheaper than burning oil or gas. One drawback with such a fuel, however, is that it deposits an ash that lays in the furnace and fuses. This requires at least a sweeping out and possibly a jack-hammer type operation which could damage the fire brick in the floor of the boiler or, worse yet, the boiler tubes underneath the floor. This also requires the boiler to be shut down and cooled off, which results in loss of use of the boiler for at least a day in order for the workman to enter the boiler and clean it out.
Heretofore, it has been the general consensus among boiler manufacturers and operating people that a flat-bottom furnace was impractical for the removal of ash on a continous basis during operation. Systems prior to this invention which had ash removal from the furnace required a hopper bottom type boiler with tubes specially bent for this purpose and a vertical flow of gases through the furnace. The problem with the hopper-bottom type boiler is that it is very expensive to build and requires a large slag tank in the bottom of the boiler which is also expensive. Hopper-bottom boiler systems usually require the vertical flow of combustion gases in the furnace. A vertical, hopper-bottom boiler system therefore generally must be built to such a size that it is very impractical, if not impossible, to prefabricate it and ship it to the site. This means that the vertical, hopper-bottom boiler system must be erected at the site where it is to be used, thus further increasing the cost of the system.
Another approach to the problem is to fire the fuel horizontally in the boiler, with the boiler having a flat bottom furnace. U.S. Pat. No. 2,097,268 illustrates such a system. Current state-of-the-art technology in burners and pulverizers has permitted the use of a single burner and a single pulverizer for capacities of up to and in excess of 100,000,000 BTU's per hour in a boiler which also have turn-down capabilities previously only possible with multiple-burner and multiple-pulverizer operations. U.S. Pat. Nos. 4,387,654; 4,310,299; and 4,184,640 disclose examples of burners and pulverizers for solid fuel. By using a single burner and a single pulverizer the capital cost of such a project is greatly reduced. Up to now, however, this technology has been hampered by the fact that this equipment is most effectively used in a horizontally-fired, flat-bottom boiler which heretofore had no means of continuous ash removal. Accordingly, as will be shown hereinafter in greater detail, the present invention complements the advances in technology in the burner and pulverizer fields.